Apparatus for determination of the temperature of deposition of electrically nonconducting solids from gases



Dec. 1. 1953 T. J. WEBSTER 2,660,882

APPARATUS FOR DETERMINATION OF THE TEMPERATURE OF DEPOSITION 0FELECTRICAL-LY NONCONDUCTING SOLIDS FROM GASES Filed April 2, 1952 2Sheets-Sheet 1.

I/VI E/VTOP THOM'A5 3 WEBSTER.

G (AM ATTORNEY 'r. J. WEBSTER 2,660,882 ETERMINATION OF THE TEMPERATUREF DEPOSITION OF ELECTRICALLY NONCONDUCTING Dec. 1, I953 AIBPARATUS FOR DA SOLIDS FROM GASES Filed April 2, 1952 2 Sheets-Sheet 2 ,8 QEEOQ H -HHI 88: U mwm I! I/VI ENTOR J-WEBSTER THOMAS Patented Dec. 1, 1953APPARATUS FOR TEMPERATURE DETERMINATION OF THE OF DEPOSITION F ELEC-TRICALLY NONCONDUCTING SOLIDS FROM GASES Thomas John Webster,

signer to The British ited, London, England Application April 2, 1952,Serial N 0. 280,116

Claims priority, application Great Britain April 9, 1951 3 Claims. (01.73-17) This invention relates to a method and apparatus for thedetermination of the temperature of deposition of an electricallynon-conducting solid from a gas, such as, for example, the determinationof the so-called ice point of a gas, that is the temperature at whichice is deposited from a gas containing Water vapour at so low aconcentration that the gas becomes saturated with water vapour at atemperature below 0 C. so that the water vapour is deposited in the formof ice when the temperature of the gas falls below its saturation point.A knowledge of the ice point allows the humidity of the gas readily tobe calculated. For the sake of clarity, the invention will throughout bedescribed with reference to the determination of the temperature ofdeposition of ice from a gas, but it will be appreciated that it maysimilarly be employed for the determination of the temperature ofdeposition of any other electrically non-conducting solid from a gas.

Hitherto, the determination of the ice point of a gas has depended uponvisual or photoelectric observation of the formation of an ice film on asuitable surface which is progressively cooled in contact with the gas.Such visual observation cannot be made with a gas at high pressure, owinto difiiculties in construction imposed by the necessity for usingtransparent materials, and in such cases it is accordingly necessary toexpand the gas to a relatively low pressure before making thedetermination, thereby decreasing the sensitivity of the method.

A further source of error in the determination lies in the fact thatcertain gases, for example, air, tend to become supersaturated withwater on being cooled below the condensation point, so that the observedice-formation takes place at a temperature below the true ice point.

It is an object of the present invention to provide an apparatus for thedetermination of the temperature of deposition of ice or otherelectrically non-conductin solid from a gas which can be used directlyfor gases either at high or low pressure and which for a considerablerange of temperatures of deposition are not subject to errors caused bysupersaturation of the gas at the condensation temperature.

It is a further object of the invention to provide an apparatus whichcan be made fully automatic in itsoperation and can be adapted tooperate continuously.

According to a further feature of the invention, apparatus for thedetermination of the temperature of deposition of ice or otherelectrically London, England, as- Oxygen Company Limnon-conducting solidfrom a gas comprises an electrical conductor arranged to form part of anelectrical circuit, means formaking and breaking the circuit at frequentintervals at the surface of the conductor, means for passing a stream ofgas over the said surface, means for progressively reducing thetemperature of the said conductor and means for recording thetemperature of the surface of the conductor exposed to the gas stream atwhich completion of the electrical circuit ceased to take place owing tothe formation of a deposit of the electrically nonconducting solid onthe surface.

The electrical conductor is preferably of metal adapted to be cooled ata controlled rate and is made to form part of an electric circuit whichis closed at frequent intervals by causing the free end of anelectrically conducting feeler, for example a metal wire, also includedin the circuit to touch the surface of the conductor exposed to the gasstream. This surface ispreferably polished or plated to ensure goodelectrical contact. The motion of the feeler towards or away from thesurface may be effected by hand or preferably mechanically, for exampleby a motor-driven cam mechanism.

The completion of the circuit may if desired be indicated each time thefeeler touches the surface by a micro-ammeter or other sensitiveelectrical device incorporated in the circuit, the temperature of thesurface being continuously measured by means of a thermocouple or othertemperature measuring device in intimate contact therewith. Inoperation, a slow stream of gas whose ice pointis to be determined ispassed over the surface of the conductor and the temperature of thelatter progressively reduced. As soon as the ice point of the gas isreached, ice begins to condense on the cooled metal surface and formedthereon an insulating layer which interferes with the circuit when thefeeler is subsequently brought into contact with the surface. Thefailure of the wire to complete the circuit as indicated by the lack ofreaction by the micro-ammeter indicates that the ice point has beenreached and the temperature of the surface at the instant when thisfailure first occurs is recorded as the ice point temperature.

Alternatively, the system can readily be made fully automatic inoperation; for example, the failure of the feeler to complete thecircuit may be made to operate an automatic temperaturerecording deviceby a suitable system of relays. Further, after recording thetemperature, the

completion of the electricalrelay system may be made to operate aheating device to raise the temperature of the surface sufliciently toremove the ice deposited thereon, and thereafter to restore the systemto its original condition. By this means, the apparatus can be adaptedautomatically to provide a continuous series of readings of the icepoint of the gas stream.

A convenient method of cooling the metal surface at a controlled rate isto form the surface at one end of a tube or rod of copper or other metalof high heat conductivity and to immerse the other end of the rod ortube in a bath of refrigerant, such as, for example, liquid oxygen orliquid nitrogen. The rate of cooling may be controlled by adjusting thedepth of immersion of the rod or tube in the refrigerant bath, or byheating an intermediate portion of the rod or tube in a controlledmanner. Alternatively, the tube or rod may consist of two sections ofcopper joined by a section, for example of brass, acting as: atherma'l'resistanee, in which case the rate of cooling will beindependent of the depth of immersion of the rod or tube in therefrigerant, so long as only the lower section of copper is so immersed.

In using the apparatus of the present invention todetermine the icepoint of a gas, it has been found that when the ice point is, belowabout -20- C. the ice film is not deposited uniformly over the whole ofthe surface of the conductor exposed to the gas stream but formspreferentially at the point of contact between the surface and thecontacting feeler. This efiectincreases considerably the sensitivity ofthe method since it localises the formation of the effective ice filmwithin a very small area. Moreover, the moving. contact tends to seedthe formation of ice crystals from the gas which prevents the gas frombecoming supersaturated with water vapour as it is cooled below thecondensation point.

Since the present method does not depend upon visual or photoelectricobservation for detection of the ice film, when the ice point of a gasat high pressure is to be determined, the detecting device may betotally enclosed within an opaque vessel constructed of material capableof withstanding the pressure of the gas. It is therefore unnecessary toexpand the gas to a low pressure before the determination and thesensitivity of the method is thereby maintained.

At atmospheric pressure it has been found that the ice point of airsaturated at a temperature as low as -l C. can be determined by themethod of the present invention within an accuracy of one or two degreescentigrade.

The invention will now be more particularly described with reference tothe accompanying drawings which illustrate one form of apparatusaccording to the invention adapted automatically to provide a continuousseries of determinations of the ice point of a gas at atmosphericpressure.

In the drawings Figure 1 shows in diagrammatic side elevation theapparatus proper; and

Figure 2 shows diagrammatically the relay system associated therewith.

Referring to Figure l, a feeler I consisting of a short length of fineplatinum wire, is attached to one end ofa thin strip 2 of springmaterial, the other end of which is adjustably fixed to one end of acam-follower 3, the relative positions ofstrip 2 and cam-follower 3being adjustable as. hereinafter described.

.. the feeler I is touching by means of a screw 4. The cam-follower 3 isformed with a right-angled bend and is mounted to pivot at the bend ona. fixed horizontal pivot 5. The feeler I: is caused to perform, a.vertical reciprocating motion by a cam 6 rotating about a. spindle Idriven by a synchronous motor (not shown) at a suitable speed, againstthe surface of which cam a projection 8 from the end of the;cam-follower 3 to which the feeler I is attached bears.

At the bottom of its stroke the feeler I makes contact with the end 9 ofa copper rod II], this contact being made at su'table intervals andmaintained for about 0.5 second. Both the feeler I. and. the rod II) areincluded in an electrical circuit. forming part of the relay system Theforce between the feeler I and the end 9 of the rod I0 may be adjusted"by means of a screw II which acts as a stop for the end of thecam-follower 3 remote from the feeler I and thus controls the positionof thelower end of the stroke. The time for which: contact is made maybe adjusted by means of the screw 4 controlling the position of thefeeler I- relative'tothe cam-follower 3. r

A second cam-follower 12', also pivoted at a right angled bend on. the.horizontal pivot 5, is provided at the end adjacent. to the. cam B witha threaded extension I3 on which works on a nut It which bears againstthe surface of the cam. The other end of. the cam-follower l2 carries anelectrical contact I5 which is caused by themovement of the. ca-fol1ower I2 to touch momentarily a screw l6, during the period whenthe. surface 9 of the rod Is; that is it makes contact after the feelerI touches the surface 9 and breaks contact before the feeler leaves thesurface. The time of operation of this contact relative to that of thefeeler i may be varied by altering the position of the nut It on thethreaded extension l3. Both the contact 15 and the. screw I6 areincluded an electrical circuit forming, part. of the relay system ashereinafter described. The cam-fol- 1owers'3, I2 are constrained tofollow the cam surface by springs t1. I8 attached to their respectivelower ends. I The surface 9 of the copper rod i is plated with rhodium.or other electrically conducting protective material to preventcorrosion and to give a good electrical contact, and acts as the coolsurface on which depositionof iceoccurs. Athermocouple l 9 passesaxially up the rod it? its operating junction being located close behindthe surface 9. The thermocouple I9 is connected to a dottin recorder ofconventional pattern (not shown) which records the temperature of thesurface 9 on a continuous motor-driven chart by means of a chopper barmechanism actuated by the relay system as hereinafter described. Aheater 2G is wound round the rod IE near the top thereof for removal offrost.

The lower end of the rod. I8 has screwed toit a brass rod 2| to which isin turn screwed a further length of copper rod 22 which is immersed.

in a liquid oxygen bath (not shown) The brass rod 2i acts as a thermalresistance so that the rate of cooling of the surface 9 is independentof the level of liquidoxygen so long as the lower section 22 of copperand this alone is immersed.

The surface 9 of therod It is enclosedin a housing 23 of a transparentmaterial which is provided with a gas entry port 26 and a gas exit 25,the latter in this example also serving as an entry for the feeler I.The housing 23 has the double function of directing the stream of gas tobe tested against the surface 9 and of excluding atmospheric air.

In operation, a stream of the gas to be tested is passed through thehousing 23 and the surface 9 is progressively cooled while the feeler Icontinues to contact the surface 9 at regular intervals, thus making andbreaking regularly the electric circuit. As soon as frost appears on thesurface 9 when the ice point is reached, the feeler can no longercomplete the circuit and a relay system is operated as hereinafterdescribed to effect the sequence of operations involving (1) recordingthe temperature, (2) thawing oif the frost and (3) re-cooling the rodI0.

This sequence is performed automatically and repeatedly by means of thecircuit shown in Fig ure 2. The relays are shown therein in the positioncorresponding to that part of the sequence during which the rod It isbeing cooled and before frost has been produced. Relay R3 is theoperating relay of a conventional post oiiice rotary selector having sixrotating contacts CI-CS, shown in the figure as each having fourpositions. These contacts are connected as follows:

Cl at the fourth position closes a circuit including the relay R3 and aswitch S3 normally closed;

C2 at the second position closes a circuit including the chopper barmotor of the temperature recording device connected directly to a mainsource of alternating current at 230 v.;

03 at the second position closes a circuit including the relay R3 and aswitch S actuated by the chopper bar of the instrument recording thetemperature of rod ID as hereinafter described;

C4 at the third position closes a circuit including the relay R3 an alsoincluding switch S5 through a conventional amplifier indicated at Awithin the panel enclosed by the broken line, the switch S6 beingoperated by the pointer of the instrument recording the temperature ofrod If! as hereinafter described;

C5 at the first position closes a circuit including switch S4, relay I2and the contacts l5 and I6; and

G6 at the second and third positions closes a circuit including theheater 2i! and a warning lamp L in parallel therewith.

Each of these circuits includes the requisite source of alternating ordirect current at the appropriate voltage, such current being obtainedfrom the main voltage source through the necessary transformers andrectifiers.

In operation, when the rod I9 is being cooled, the contacts CI-CES willbe in the position shown in the diagram. When the feeler 4 makes contactwith the surface 9 of the rod I3, it completes a circuit including themoving-coil relay MMCR which opens switch S4 in series with the contactI5, so that when contacts I5 and I 6 touch during the period when thefeeler I and surface 9 are in contact as hereinbefore described, nocurrent flows through the circuit including contact C5. When frost firstappears on the surface 9, however, the feeler I does not make electricalcontact with the surface 9 so that switch S4 remains closed; hence whenthe contact I5 touches the screw I6 the circuit including contact C5 iscompleted energising relay R2.

Relay R2 closes switch 82 thus in turn energising relay R3 which movesthe contacts C1-C6 to the second position, and at the same time opensswitch S3 which de-energises relay R3. Contacts C6 and C2 switch on theheater 20 and the chopper bar motor respectively. When one dot recordingthe temperature of the surface 9 has been recorded, the movement of thechopper bar closes the switch S5 which is coupled thereto and completesthe circuit through contact C3 again energising relay R3 and moving thecontacts Cl-C6 into the third position.

During this period the heater remains on until the temperature of therod II! has been raised to a predetermined value at which all the frosthas been evaporated from surface 9, when the switch S6 attached to thepointer of the temperature recording instrument closes and operates therelay R3 through the amplifier A. The contacts CI-Cfi are moved to thefourth position when contact CI completes a circuit again energisingrelay R3 and thus restoring the contacts Cl-CB to the first position andthe system to its initial condition.

By the use of this instrument a series of readings Of the ice point ofthe gas stream can be taken automatically over as long a period as maybe desired.

I claim:

1. Apparatus for the determination of the temperature of deposition ofan electrically nonconducting solid from a gas which comprises anelectrical conductor arranged to form part of an electric circuit, anelectrically conducting feeler also included in said electric circuit,means for making and breaking contact between the surface of saidconductor and an end of said feeler at frequent intervals thereby makingand breaking the circuit at frequent intervals at the surface of theconductor, means for passing a stream of the gas over the said surface,means for progressively reducing the temperature of said sursaidsurface, temperature recording means, and relay means operableautomatically on the failure perature at which such failure 3. Apparatusoccurs. for the determination of the deposition of an electrically nonconducting solid from a gas which comprises an electrical conductorarranged to form part of ice pregressivelyreducin th -tempe atu e 0f thesaid-surface, t mp ratur r c rding mea heating means jor raising thetemperature of said conductor, and relay means operable automatically onthe failure of the circuit to be completed Owing to the formation of adeposit of the electrically non-conducting solid on said surface firstto actuate said temperature recording means to record the temperature atwhich such failure occurs and thereafter to actuate said 10 heatingmeans until the temperature of said suriaee has been raised to apredetermined value sufiiciently high to ensure that all theelectrically non-conducting solid deposited on said surrace-has beenevaporated therefmmand thereafter to .de-activate said heating means.

THOMAS JOHN WEBSTER.

References Cited in the file of this patent Number Number UNITED STATESPATENTS Great Britain Aug. 12, 1929

